Regenerator heat exchange devices or regenerators are well known. One type of regenerator is the rotary air-to-air heat exchanger, which is typically in the form of a rotary heat exchange wheel including a matrix of heat exchange material. For example, see Canadian Patent No. 1,200,237 (Hoagland), U.S. Pat. Nos. 4,432,409 (Steele) and 4,875,520 (Steele et al.), and pending U.S. patent application Ser. No. 08/736,382, filed Oct. 24, 1996, filed in the names of Donald F. Steele and Lawrence C. Hoagland, entitled Regenerator Heat Exchanger Having One or More Adjustable Performance Characteristics and assigned to the present assignee (hereafter the "Co-pending Application"), which application is a continuation-in-part of Ser. No. 08/132,523 filed Oct. 6, 1993, now abandoned, all assigned to the present assignee and incorporated herein by reference. Rotary air-to-air heat exchangers transfer sensible heat and moisture, usually between ducted and counterflowing airstreams, for the purpose of conserving energy within a building, while providing outdoor air ventilation to remove air pollutants from a building. For example, heat and moisture from indoor air being exhausted to the outdoors during the heating season are transferred to the cooler, dryer incoming fresh air, and during the cooling season, heat and moisture from entering warm moist outdoor air are transferred to the cooler drier air as it is exhausted to the outdoors. Transfer of heat and moisture in this manner can typically reduce the amount of energy required to heat, cool, humidify or dehumidify the incoming ventilation air typically anywhere between about 50% and about 85%, depending primarily on the performance characteristics of the rotary energy transfer wheel.
It is well known to make such rotary heat exchange wheels with a matrix of heat exchange material (capable of absorbing sensible heat) coated with a desiccant material (capable of absorbing moisture and thus latent as well as sensible heat). Such regenerators are used in ventilation systems, such as provided in energy recovery ventilators or in heating and/or air conditioning systems, in which the transfer of both sensible and latent heat is desired as, for example, in the case of air conditioning systems used in summer climates characterized by hot and humid outdoor air. In such climates, it is often desirable to bring fresh air in from the outdoors. In this case the regenerators are used to transfer sensible and latent heat from incoming air to the outgoing air. The removal of latent heat from incoming air prior to passing the air over evaporation coils of an air conditioning system helps reduce the heat load imposed on the air conditioning system.
To achieve maximum latent heat transfer, as is well known in the prior art, a suitable sensible heat exchange matrix material such as plastic (i.e., high molecular weight, synthetic polymers), aluminum, or Kraft or other fibrous paper is completely and uniformly coated with a desiccant material in accordance with processes known to those skilled in the art. In one type of regenerator, the matrix comprises a plastic strip coated with a desiccant material wound around a hub so as to form a heat exchange wheel. The airflow through the wheel, and the efficiency of heat transfer by the wheel matrix, are determined in part by the spacing between opposing surfaces of adjacent portions of the strips of the matrix. This spacing can be controlled by controlling the height of embossments in the strip. For a given air flow, the tighter the spacing (or the denser the wrap), the higher the efficiency of heat exchange matrix and the greater the pressure drop across the two sides of the wheel. See U.S. Pat. Nos. 4,432,409 to Steele and 4,825,936 to Hoagland et al.
There has been a trend toward the requirement for increased ventilation rates to decrease indoor air pollutants. These larger ventilation rates necessarily require larger energy recovery wheels. As the wheels have increased in size, they have increased in weight so that it has become desirable to manufacture the wheel in wedge-shaped segments (typically eight segments, each subtending a 45.degree. angle) and mount the segments in a wheel frame so that the wedge-shaped segments can each be separately mounted in the frame and removed for cleaning and/or replacement.
The wedge-shaped segments have worked well for wheels as large as 74 inches in diameter. However, wheels of even larger dimension are required, e.g., wheels having diameters on the order of 104 inches and larger. Increasing the wheel to this size creates problems. One problem relates to the wheel frame. The forces of the increased counterflowing air can provide bending moments to the larger wheel frame, which in turn can cause distortion of the wheel, as well as leaks around the periphery of the wheel. In addition, the increased weight of each wedge-shaped segment makes it relatively heavy and difficult to assemble in the wheel frame, and remove from the wheel frame for cleaning and replacement. For example, a wedge-shaped wheel segment made of plastic strips coated with a desiccant material, subtending a 45.degree. angle, and designed for a 104 inch wheel would weigh on the order of 60 pounds or more depending on the thickness of the wheel. This is particularly a problem in the field, where commercial ventilation systems are typically mounted on the roofs of buildings making it difficult to service the wheels. In some designs it is necessary to remove the wheels with heavy equipment, making it often impractical to replace the wheel, and thus providing little incentive to do so.
Accordingly, the objects of the invention are to provide an improved rotary heat regenerator wheel assembly: (a) with an improved and stronger wheel frame assembly for supporting segments, (b) which is easy to assemble and disassemble, and (c) which includes differently shaped segments so that the segments can be of a reduced size to facilitate mounting and removing them from the frame, and cleaning and replacing them.